A liquid crystal display device (hereinafter referred to as LCD) is an element for displaying characters and images by utilizing electrooptical properties of a liquid crystal molecule, and spreads widely in portable telephones, notebook computers and liquid crystal televisions. However, LCD utilizes a liquid crystal molecule having optical anisotropy, so that there is a problem that excellent display properties are exhibited in one direction, while a screen becomes dark and unclear in other directions.
Hitherto, as a retardation film, a retardation film having a characteristic, in which a retardation value measured by light with a short wavelength is smaller than that measured by light with a long wavelength (also referred to a reverse wavelength dispersion characteristic) has been developed (Patent Document 1).
However, since the above-mentioned conventional retardation film has a relatively small birefringence in a plane, a thick film have to be formed in order to exhibit a desired retardation value. Furthermore, the difference between a retardation value on the short wavelength side and a retardation value on the long wavelength side is relatively small, and therefore, a further improvement in a wavelength dispersion characteristic of the retardation value is required.
In addition, a retardation film, in which a polymer having an acetal structure having an aromatic group as a side chain is used, is also known (Patent Document 2). This retardation film is preferable since it exhibits a reverse wavelength dispersion characteristic.
However, when the polymer disclosed in Patent Document 2 is used, it is not necessarily possible to obtain a retardation film having a large in-plane birefringence or a retardation film in which the difference between a retardation value on the short wavelength side and a retardation value on the long wavelength side is large. Therefore, further improvements in the above-mentioned issues are required.    [Patent Document 1] International Publication WO 00/26705    [Patent Document 2] Japanese Unexamined Patent Publication No. 2006-65258